Ms Rudd said: "We are making sure that the parts of the NHS that have been impacted have the support they need to make sure that patient data hasn't been accessed, and the reassurance we've received from them on the front line is that that is currently the state of play."

But despite the home secretary's assurances, patient data remains inaccessible in many instances and the health service faces a weekend of chaos as IT experts try to restore vital computer systems.

Ms Rudd stressed the malware assault on the NHS had been part of a major international attack and insisted that Britain was at the forefront of tackling such attacks.

"In fact the response has been good in the UK, and I hope we will be able to continue to disrupt it," she said.

The malware programme that has caused such chaos for the NHS and affected businesses in more than 70 countries exploits a security loophole in Microsoft XP software.

Asked why the government allowed the NHS to operate software that is no longer supported by Microsoft, Ms Rudd said that Jeremy Hunt, the secretary of state for health, had been "clear" that the NHS had been asked to upgrade its software.

Jeremy Hunt has been accused of ignoring warning signs the NHS was vulnerable to cyber attack Credit: PA

Mr Hunt has found himself under fire as a result of the cyber attack, with shadow health secretary Jonathan Ashworth accusing him of ignoring "extensive warning signs" of the health service's vulnerability.

In a letter to Mr Hunt on Saturday Mr Ashworth said there had been repeated warnings about the outdated NHS systems, including from the National Cyber Security Centre (NCSC) and the National Crime Agency (NCA).

"NHS Trusts have been running thousands of outdated and unsupported Windows XP machines despite the government ending its annual £5.5 million deal with Microsoft, which provided ongoing security support for Windows XP, in May 2015," Mr Ashworth wrote.

"It effectively means that unless individual trusts were willing to pay Microsoft for an extended support deal, since May 2015 their operating systems have been extremely vulnerable to being hacked," he added.

He said a Freedom of Information Request in February had found a total of 79 English NHS trusts have suffered ransomware attacks since June 2015.